In such a method disclosed in U.S. Pat. No. 3,669,093, the front end of the tube is placed in position as best as can be done, after which the transport member disposed behind the shielding block transports the radioactive material to the target area. During this transport, only a check of the end positions of the transport thread takes place by checking the place of the end of the transport thread by means of two spaced apart photoelectric cells.
It will be clear that this system offers no guarantee whatever for the arrival in the target area of the radioactive material present at the front end of the thread; for instance, a kink may occur in the tube during its movement via e.g. the windpipe to the target area, in this case the lungs.